Acoustical loud speakers



Feb. 25, 1964 A. ROBBINS ACOUSTICAL LOUD SPEAKERS 2 Sheets-Sheet 1 FiledAug. 25. 1961 ATTORNEY Feb. 25, 1964 v A. ROBBINS 3,122,214

ACOUSTICAL LOUD SPEAKERS Filed Aug. 25, 1961 2 Sheets-Sheet 2 mm. FIG. 4a

E lll 28 FIGS INVENTOR.

M4 @564 BMJQW 143% ATTOR N EY United States Patent 3,122,214 ACOUSTICALLOUD SPEAKERS Alex Robbins, Long Island City, N.Y., assignor to StandardSystems C'orp., Long Island City, N.Y., a corporation of Delaware FiledAug. 25, 1961, Ser. No. 133,839

10 Claims. (Cl. 181-31) This invention relates to acousticalloudspeakers.

It is well known that a cone. loudspeaker produces a normal directivitypattern which is acceptably wide at low frequencies. However, thedirectivity increases at the higher frequencies. In fact, while at thelow frequencies it may be considered that a small loudspeaker willradiate sound of a few hundred cycles in a 180 pattern, at about 10,000cycles the lobe narrows down to about 22". Accordingly, only listenersin front of the speaker will hear the high frequencies while those tothe side will not.

While various schemes have been devised in order to improve sounddistributions at high frequencies, they have been generally ineffective.

With the foregoing in mind, I have devised a loud-.

speaker which will provide a wide and uniform distribution pattern oversubstantially the whole audible range of frequencies. This isaccomplished by incorporating a horn configuration in connection withthe baffle plate or loudspeaker mounting, wherein the higher frequenciesmay be diverted and transmitted through the horn and then radiated sothat their pattern is substantially coextensive with the acceptably widelow frequency radiation pattern.

Although I have referred to the configuration of my structure as that ofa horn, actually, it simply involves the formation of a horn-shapedinterior channel formed in or adjacent to the baffle structure. It iswell understood that high frequencies radiate from the cone fromsubstantially a point source, i.e., at or around the center of the cone.Stated in other words, it may be said that the output of a loudspeakeralong its axis will be accentuated at the high frequencies. However, byintercepting and diverting the high frequency energy to a channelserving as a horn structure, the source may be considerably enlarged,i.e., the mouth of the horn, so that we no longer have a point oraxialsource of radiation but an elongated mouth source which tends to enlargethe pattern and make it substantially equal and coextensive with the lowfrequency radiation pattern.

Of course, it may be understood that in using my structure, the listenermay find it desirable to increase the volume of the high frequencyoutput so as to compensate for any losses occasioned by diverting andchanneling the high frequencies. However, as I will show herein, thatobjective may be realized by providing a perforated outer grilledesigned to discriminate against the higher frequencies. Accordingly,the grille itself may serve as an effective diverter of higherfrequencies to be channeled through the horn structure.

The invention will be further understood from the following descriptionand drawings in which:

FIG. 1 is a cross-sectional view taken substantially alongthe line 1--1of FIG. 4;

FIG. 2 is an exploded view of the elements of the loudspeaker;

FIG. 3 is a cross-sectional view as taken along the 7 line 33 of FIG. 1;

FIG. 4 is a front view of the loudspeaker, partly broken away;

FIG. 5 is a fragmentary, partly cross-sectional view of a modifiedembodiment; and

' FIG. 6 is a front view of the central deflector member taken along theline 66 of FIGURE 5.

3,122,214 Patented Feb. 25, 1964 Referring to FIGURES 1-4, the deviceincludes a conventional box 10 which may be of any standard size,configuration and fabrication. It is formed with the usual flange 11 forsupporting the loudspeaker baffle.

The loudspeaker actuating or driving unit 12, its frame 13, and itsdiaphragm or cone 14 are all conventional, Its front mounting bafiie 15has the usual speaker opening 16 which, in the instant device, issomewhat olfset from the center of the bafiie to provide more space forthe horn structure and its mouth, as will be hereinafter described. 1

Secured, as by adhesive or otherwise, to baflie 15, is the forward panel17. Forward panel 17 may be typically from about /2 to 2 inches thickalthough its thickness is widely variable. It may be formed of wood orany other solid material but it is advantageously fonned of acompressible material such as natural or synthetic sponge rubber orsponge plastic. This will provide a damping effect and avoid undesirableresonance. Further, such a forward panel may easily be compressed so asto vary the effective thickness thereof and thus vary the cross sectionor thickness of the horn structure as will be clear hereinafter. I

Forward panel 17 is formed with a circular main opening 18 which iscoincident with baiiie opening 16 so as to radiate outwardly sound wavesgenerated by the diaphragm 14. It is also formed with a horn-shapedopening 19 laterally of and communicating with opening 18 at restrictedthroat 25).

It will be evident that opening 19 forms a horn-shaped duct incooperation with baflie 15 which it abuts. As will hereinafter appear,this lateral opening or duct 19 transmits high frequency sound wavestherethrough to be radiated from an elongated source represented by themouth of opening 19.

Opening or duct 19 flares outwardly substantially exponentially from itsinner throat 20 to its elongated, substantially rectangular mouth 21.Month 21 is formed by covering all of the top or front of opening 19 asby panel 22, while still leaving exposed mouth 21 as noted in FIG. 4.

Panel 22 is, in fact, integral with deflector arm 23, these two elementsjointly being somewhat T-shaped. Deflector arm 23 is semi-cylindrical orconcavo-convex in cross section. [It lies inclined as illustrated inFIG. 1 with its inner end 24 disposed adjacent to the inner cen tralportion of the diaphragm 14 and its other end 25 disposed at throat 20.Accordingly, it serves the function of channeling sound waves,particularly in the higher frequencies, to throat 20 and through duct 19to be radiated through mouth 21. i

Panel 22, in partially covering duct 19, defines the width and depth ofmouth 21which may typically be from about /2 to 2 inches, andits lengthfrom about 8 to 18 inches although these dimensions are purelyrepresentative and are not critical. At the smallest dimensions abovementioned, the duct or horn will have a low frequency cut-off of about700 cycles, so as to discriminate against such lower frequencies andfavor the transmission of higher frequencies.

A perforated grille 26 covers panel 17 as well as panel 22 and arm 23.Grille 26 may be of conventional fabrication, i.e., a perforated sheetof the usual materials. It need not have special acoustical propertieswhen it is formed with a cut-out 27 coincident with mouth 21. In fact,this cut-out 27 may be eliminated and the grille 26 may take the form ofan unbroken although perforated sheet as will be evident. However,cut-out 27 is advantageously employed when grille 26 is fabricated ofmaterial presenting a resistance to the transmission of the higherfrequencies. Such construction is well known. The reactive acousticalimpedance of a perforated sheet may vary with frequency by selecting thesizes of the perforations and thickness of the sheet, all as set forthin the book Acoustics, by Beranek (McGraw-Hill, 1954). In fact, whenusing such a sheet, provided with cut-out 27, the deflector arm 23 may,if desired, be dispensed with since the sheet or grille itself willfavor the transmission of low frequencies and the partial rejection andchanneling of high frequencies through the cut-out 27.

Finally, a conventional frame 28 may embrace the grille margin as wellas the margins of baffle 1'5 and panel 17.

FIGURES 5 and 6 show a modified embodiment, eliminating the deflectorarm 23 and the panel 22. The grille 26a may be substantiallynon-discriminatory in frequency in which case it will cover the mouth 21as illustrated. in the place of the deflector arm 23 is the simpledeflector member 29 having one end simply secured, as by adhesive or astaple, to the center of the inner surface of grille 26a. Member 29 isimperforate and simply comprises a sheet Whose free end is curved towardthe recessed center of diaphragm 14. Its function is to divert orchannel sound waves, particularly in the higher frequencies, toward andinto the duct 19 for radiation through mouth 21.

From the foregoing, it will be seen that I have provided a device todivert higher frequencies toward a separate duct and mouth so as tosomewhat equalize the radiation patterns of the high and lowfrequencies. Essentially a deflector is used near the center of thediaphragm. The fact that output from a loudspeaker shows an accentuationat the high frequencies along its axis, is confirmed by the bookElements of Acoustical Engineering by Olson (Van Nostrand, 1947).Further, by using a grille exhibiting a reactive acoustical impedance,and providing a cutout therein at the mouth of the duct, even a de ectormay be eliminated. The grille itself will serve as an interceptor ofhigh frequencies which will be diverted through the duct.

1 have shown preferred embodiments of my invention but it is obviousthat numerous changes and omissions may be made without departing fromthe spirit thereof. For example, the duct 19 need not be uniform incrosssection but may have a narrow throat area and a wide mouth area, orany other desired variation thereof.

What is claimed is:

l. A loudspeaker comprising a diaphragm member, actuating meanstherefor, and a forward mounting therefor, said forward mountingcomprising a baflle secured forwardly of said diaphragm member, a panelsecured to and forwardly of said bafile, said forward panel having amain opening for directly forwardly radiating sound waves generated bysaid diaphragm member and further having a horn-like lateral openingformed therethrough communicating with said mm'n opening, and a frontpanel member secured to said forward panel whereby to form, incooperation with said baffle, an intermediate duct from said horn-likelateral opening, said duct having a restricted throat which is disposedat and in communication with said main opening and an elongated mouthlaterally of said throat for radiating at least some sound wavesgenerated by said diaphragm member.

2. A loudspeaker according to claim 1 and wherein said forwardly securedpanel is fabricated of a compressible material.

3. A loudspeaker according to claim 2 and wherein said front panelmember comprises a perforated grille.

4. A loudspeaker according to claim 1 and including a deflector armhaving one end thereof disposed adjacent to an inner central portion ofsaid main opening and its other end disposed at said throat so as tochannel sound waves to said throat and through said duct.

5. A loudspeaker according to claim 4 and wherein said deflector arm issemi-cylindrical, said one end thereof comprising a mouth directedtoward the center of said diaphragm member for diverting high frequencysound waves along said deflector arm for channeling through said duct.

6. A loudspeaker according to claim 1 and including a deflector memberdisposed centrally inwardly of said restricted throat for interceptingsound waves for diversion and transmission through said duct.

7. In a loudspeaker including a diaphragm member and actuating meanstherefor, a panel secured forwardly of said diaphragm member and havinga main opening therethrough for radiating sound Waves generated by saiddiaphragm member, said forwardly secured panel being further formed witha lateral duct communicating with said main opening whereby at leastsome of said sound waves may be diverted through said duct, said ducthaving an elongated mouth disposed laterally of said main opening forradiating said diverted sound waves, and a perforated grille connectedforwardly of said forwardly secured panel, said grille having a reactiveacoustical impedance whereby higher frequencies in the audio range maybe substantially intercepted and diverted thereby to and through saidduct.

8. The combination according to claim 7 and wherein said grille isformed with a lateral, elongated opening coextensive with said elongatedmouth.

9. The combination according to claim 8 and including a deflector armhaving a free end thereof disposed adjacent to an inner central portionof said diaphragm member, and a duct cover integral with said deflectorarm.

10. The combination according to claim'9 and wherein said duct has a lowfrequency cut-off of about 700 cycles so as to radiate substantiallyonly sound waves of fre quencies above 70G cycles.

References Qited in the file of this patent UNITED STATES PATENTS2,035,108 Weil Mar. 24, 1936 2,102,212 Olson Dec. 14, 1937 2,386,996Williams Oct. 16, 1945 2,885,024 Jordan May 5, 1959 2,979,150 Irby Apr.11, 1961

1. A LOUDSPEAKER COMPRISING A DIAPHRAGM MEMBER, ACTUATING MEANSTHEREFOR, AND A FORWARD MOUNTING THEREFOR, SAID FORWARD MOUNTINGCOMPRISING A BAFFLE SECURED FORWARDLY OF SAID DIAPHRAGM MEMBER, A PANELSECURED TO AND FORWARDLY OF SAID BAFFLE, SAID FORWARD PANEL HAVING AMAIN OPENING FOR DIRECTLY FORWARDLY RADIATING SOUND WAVES GENERATED BYSAID DIAPHRAGM MEMBER AND FURTHER HAVING A HORN-LIKE LATERAL OPENINGFORMED THERETHROUGH COMMUNICATING WITH SAID MAIN OPENING, AND A FRONTPANEL MEMBER SECURED TO SAID FORWARD PANEL WHEREBY TO FORM, INCOOPERATION WITH SAID BAFFLE, AN INTERMEDIATE DUCT FROM SAID HORN-LIKELATERAL OPENING, SAID DUCT HAVING A RESTRICTED THROAT WHICH IS DISPOSEDAT AND IN COMMUNICATION WITH SAID MAIN OPENING AND AN ELONGATED MOUTHLATERALLY OF SAID THROAT FOR RADIATING AT LEAST SOME SOUND WAVESGENERATED BY SAID DIAPHRAGM MEMBER.